1. Field of the Invention
The present invention relates to a power transmission device and a wireless power transmission system that uses the power transmission device.
2. Description of the Related Art
A non-contact power feeding technology that enables power supply in a non-contact manner from the outside to, for example, electric cars or mobile devices without using a power cable has been attracting attention.
In Japanese Unexamined Patent Application Publication No. 2010-233442, a non-contact power feeding device is proposed that includes impedance detection means that detects impedance which is defined as seen from the power feeding side in a predetermined frequency range and frequency change means that sets a frequency of alternating current (AC) power. The frequency change means sets the frequency of AC power in response to a value of the impedance detected by the impedance detection means in the predetermined frequency range. Specifically, in the predetermined frequency range, the frequency change means sets the frequency of AC power to a frequency at which the phase of the impedance is zero or to a frequency at which the absolute value of the impedance is a minimum.